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dc.contributor.advisorHochgreb, Simone
dc.contributor.authorSweeney, Mark
dc.description.abstractThe influence of stratification on the structure of turbulent methane/air combustion is investigated using experimental data from laboratory scale burners: a weakly turbulent slot burner, and a higher turbulence co-annular swirl burner. The degree of stratification can be controlled independently of the overall fuel/air flow rate. The resulting measurements of scalar and velocity fields provide detailed test cases for existing and emerging turbulent flame models, covering a range of u'/sL from 1 to 10, turbulence intensities from 5% to 60%, and stratification ratios from 1 to 3. Simultaneous Rayleigh/Raman/CO-LIF measurements of temperature and major species concentrations - CH4, CO2, CO, H2, H2O and O2 - along a line are used to investigate the structure of a series of flames in both the slot and swirl burners. Concurrent cross-planar OH-PLIF allows thermal gradients to be angle corrected to their three-dimensional values. Finally, non-reacting and reacting velocity fields complete the flame database. The behavior of major species concentrations in the slot and swirl burner with respect to temperature is found to agree well on the mean with unstrained premixed laminar flame calculations. Scalar means conditioned on stoichiometry also show good agreement, aside from hydrogen which is enhanced under stratified conditions. Surface density function and scalar dissipation are lower than calculated values in all cases, suggesting that turbulence-induced thickening dominates the effect of increased strain. Metrics commonly used to derive flame surface density (FSD) were investigated. FSD may be determined using a statistical method based on measurements of temperature and its gradient, or a geometric method based on 2D temperature or LIF imaging. A third metric, an extension of the geometric method, is proposed. Good agreement is observed between the three metrics. The current database provides the first detailed high resolution scalar measurements for premixed and stratified flames. The data analysis provides insight into the physics of stratification: for the flames considered, the effects of stratification appear to be surprisingly small compared to those of turbulence, even at significant stratification ratios. The datasets provide a means of validating current and future computational turbulent combustion models.en_GB
dc.description.sponsorshipWork at Sandia National Laboratories was supported by the United States Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences [contract DE-AC04-94-AL85000].en_GB
dc.rightsAttribution-NonCommercial-NoDerivs 2.0 UK: England & Walesen
dc.subjectSwirl burneren_GB
dc.subjectSlot burneren_GB
dc.subjectWeaky turbulenten_GB
dc.subjectLaser diagnosticsen_GB
dc.subjectFlame surface densityen_GB
dc.subjectScalar dissipation rateen_GB
dc.subjectSurface density functionen_GB
dc.subjectFlame thicknessen_GB
dc.subjectDifferential diffusionen_GB
dc.titleMeasurements of the structure of turbulent premixed and stratified methane/air flamesen_GB
dc.type.qualificationnameDoctor of Philosophy (PhD)
dc.publisher.institutionUniversity of Cambridgeen_GB
dc.publisher.departmentDepartment of Engineeringen_GB

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Attribution-NonCommercial-NoDerivs 2.0 UK: England & Wales
Except where otherwise noted, this item's licence is described as Attribution-NonCommercial-NoDerivs 2.0 UK: England & Wales